Six-speed powertrain of an automatic transmission

ABSTRACT

Durability and power transmission efficiency are enhanced in a six-speed powertrain of an automatic transmission by a scheme that includes first to fourth planetary gearsets respectively having operational elements of a sun gear, a ring gear, and a carrier, in which the operational elements of the planetary gearsets are wisely interconnected therebetween or with an input shaft or the transmission case directly or via a clutch or a brake.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2004-0071081 filed in the Korean IntellectualProperty Office on Sep. 7, 2004, the entire content of which isincorporated herein by reference.

FIELD OF THE INVENTION

Generally, the present invention relates to an automatic transmission.More particularly, the present invention relates to a powertrain of anautomatic transmission that realizes multiple shift speeds with acombination of a plurality of planetary gearsets.

BACKGROUND OF THE INVENTION

A typical shift mechanism of an automatic transmission utilizes acombination of a plurality of planetary gearsets. A powertrain of suchan automatic transmission that includes the plurality of planetarygearsets changes rotating speed and torque received from a torqueconverter of the automatic transmission, and accordingly changes andtransmits the changed torque to an output shaft.

It is well known that when a transmission realizes a greater number ofshift speeds, speed ratios of the transmission can be more optimallydesigned and therefore a vehicle can have better fuel mileage and betterperformance. For that reason, an automatic transmission that enablesmore shift speeds is under constant investigation.

In addition, with the same number of speeds, features of a powertrainsuch as durability, efficiency in power transmission, and size depend alot on the layout of combined planetary gearsets. Therefore, designs fora combining structure of a powertrain are also under constantinvestigation.

A manual transmission that has too many speeds causes inconvenience ofexcessively frequent shifting operations to a driver. Therefore, thepositive features of more shift-speeds are more important for automatictransmissions because an automatic transmission automatically controlsshifting operations basically without needing manual operation.

In addition to various developments regarding four and five speedpowertrains, powertrains of automatic transmissions realizing sixforward speeds and one reverse speed have recently been introduced, anexample of which is found in U.S. Pat. No. 6,071,208 that was issued onJun. 6, 2000.

FIG. 15 illustrates a powertrain of the U.S. Pat. No. 6,071,208, andFIG. 16 shows an operational chart for the powertrain.

Referring to FIG. 15, the powertrain of the U.S. Pat. No. 6,071,208includes a double pinion planetary gearset PG1 and a pair of singlepinion planetary gearsets PG2 and PG3. A first carrier 4 is fixedlyconnected to an input shaft 2, and a second carrier 22 always acts as anoutput element.

Regarding connections between operational elements, a first ring gear 6and a third ring gear 8, a second sun gear 12 and a third sun gear 10,and a second ring gear 16 and a third carrier 14 are fixedlyinterconnected, respectively. Meanwhile, the first carrier 4 is variablyconnected to a first sun gear 18 and the third carrier 14 interposing afirst clutch C1 and a second clutch C2, respectively.

In addition, the powertrain further includes a first brake B1 that canstop rotation of the fixedly connected second and third sun gears 12 and10, a second brake B2 that can stop rotation of the third carrier 14, athird brake B3 that can stop rotation of the first and third ring gears6 and 8, and a fourth brake B4 that can stop the first sun gear 18.

As described above, the six-speed powertrain of U.S. Pat. No. 6,071,208includes six friction elements of two clutches and four brakes. However,it is preferable to use fewer friction elements to enable six forwardspeeds and one reverse speed so that an automatic transmission can bemore light and compact.

FIG. 16 is an operational chart for the powertrain of U.S. Pat. No.6,071,208, and FIG. 17A-17F are charts showing operation states obtainedwhen the powertrain is operated according to the operational chart inFIG. 16.

In particular, FIG. 17A shows detailed specifications of the powertrainof U.S. Pat. No. 6,071,208, i.e., gear ratios of each planetary gearset.FIG. 17B shows speed ratios in each shift-speed of the powertrainobtained by the detailed specification of FIG. 17A. In addition, FIG.17C shows rotation speeds of each operational element relative to thatof the input element, for each shift-speed. FIG. 17D shows slip speedsof friction elements at each shift-speed. FIG. 17E shows torque loadsthat each operational element or each friction element undertakes. FIG.17F shows planetary gearsets that take part in power transmission ineach shift-speed.

As shown in FIG. 16, the powertrain of U.S. Pat. No. 6,071,208 operatesthe first and fourth brakes B1 and B4 at a first speed, the first clutchC1 and the first brake B1 at a second speed, the second clutch C2 andthe first brake B1 at a third speed, the first and second clutches C1and C2 at a fourth speed, the second clutch C2 and the fourth brake B4at a fifth speed, and the second clutch C2 and the third brake B3 at asixth speed, respectively. The second and fourth brakes B2 and B4 areoperated at a reverse speed.

Referring to the operational chart, the operation state of eachoperational element of the powertrain of U.S. Pat. No. 6,071,208 isdescribed in detail. The planetary gearsets of the powertrain aresupposed to have gear ratios shown in FIG. 17A such that the speedratios shown in FIG. 17B are achieved.

(1) At the third forward speed, the first sun gear 18 rotates at a speedof more than twice that of the rotation speed of the input shaft (referto FIG. 17C). In addition, the slip speed of the fourth brake B4, whichis not operated in the third speed, becomes as high as that of the firstsun gear 18 (refer to FIG. 17D).

The third forward speed is frequently engaged in the case thatacceleration is needed, since a six-speed automatic transmission usuallyachieves the speed ratio of 1:1 at the fourth forward speed. Therefore,durability of an automatic transmission deteriorates if an elementalways rotates at a high speed in such a shift speed.

(2) Referring to FIG. 17D, slip speeds of friction elements areexcessive for all speed ranges, which deteriorates durability of anautomatic transmission and also causes excessive power loss. Therefore,the powertrain should be improved to have lesser slip speeds of frictionelements for speeds D2-D6.

In particular, the sum of slip speeds of friction elements becomesexcessively large at the sixth forward speed D6, and therefore, thedurability problem is at its maximum at the sixth forward speed.

(3) Referring to FIG. 17F, when considering the number of planetarygearsets that take part in power transmission, at least two planetarygearsets take part in the power transmission for the fifth and sixthspeeds, which deteriorates power efficiency. It is preferable thatefficiency of power transmission is improved.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the background of the inventionand should not be taken as an acknowledgement or any form of suggestionthat this information forms the prior art that is already known in thiscountry to a person of ordinary skill in the art.

SUMMARY OF THE INVENTION

As described above, a six-speed powertrain of the prior art has manyfactors to be improved. The present invention has been made in an effortto provide a six-speed powertrain having stability and durability byhaving a small number of frictional elements.

An exemplary six-speed powertrain of an automatic transmission accordingto an embodiment of the present invention includes: a first planetarygearset having operational elements of a first sun gear, a first ringgear, and a first carrier; a second planetary gearset having operationalelements of a second sun gear, a second ring gear, and a second carrier;a third planetary gearset having operational elements of a third sungear, a third ring gear, and a third carrier; a fourth planetary gearsethaving operational elements of a fourth sun gear, a fourth ring gear,and a fourth carrier; an input shaft; an output gear; and a transmissioncase.

The first ring gear is fixedly connected to the third carrier and thefourth ring gear. The first carrier is fixedly connected to the fourthcarrier. The second carrier is fixedly connected to the third ring gear.The second ring gear is always stationary by being fixedly connected tothe transmission case. The third sun gear always acts as an inputelement by being fixedly connected to the input shaft. The third carrieralways acts as an output element by being fixedly connected to theoutput gear. The fourth sun gear is variably connected to the inputshaft via a first clutch. At least one of the fixedly connected firstand fourth carriers is variably connected to the input shaft via asecond clutch. The first sun gear is variably connected to the secondsun gear via a third clutch. At least one of the fixedly connected firstand fourth carriers is variably connected to the transmission case via afirst brake and is subject to a stopping operation of the first brake.The first sun gear is variably connected to the transmission case via asecond brake and is subject to a stopping operation of the second brake.

In a further embodiment, the first, second, third, and fourth planetarygearsets are disposed in a sequence of the second planetary gearset, thefirst planetary gearset, the fourth planetary gearset, and the thirdplanetary gearset.

In a still further embodiment, the first operational element of thefirst planetary gearset is integrally formed with the tenth operationalelement of the fourth planetary gearset, and the second operationalelement of the first planetary gearset is integrally formed with theeleventh operational element of the fourth planetary gearset, such thatthe first and fourth planetary gearsets form a compound planetarygearset.

Regarding such an exemplary six-speed powertrain of an automatictransmission, arrangement of the input shaft, the output gear, and thefirst to third clutches may be variously changed.

As a first example, the input shaft is disposed in a same direction ofthe output gear with respect to the third planetary gearset, one of thefirst and second clutches is disposed toward the input shaft withrespect to the third planetary gearset, and another one of the first andsecond clutches is disposed opposite of the input shaft with respect tothe second planetary gearset.

In this case, the first clutch may be disposed toward the input shaftwith respect to the third planetary gearset, and the second clutch maybe disposed opposite of the input shaft with respect to the secondplanetary gearset.

As a second example, the input shaft is disposed in a same direction ofthe output gear with respect to the third planetary gearset, and both ofthe first and second clutches are disposed toward the input shaft withrespect to the third planetary gearset.

In this case, the first and second clutches may be disposed in asequence of the first clutch and the second clutch, in a direction fromthe third planetary gearset to the input shaft.

Alternatively in this case, the first and second clutches may bedisposed in a sequence of the second clutch and the first clutch, in adirection from the third planetary gearset to the input shaft.

As a third example, the input shaft is disposed opposite of the outputgear with respect to the second planetary gearset, and both of the firstand second clutches are disposed toward the input shaft with respect tothe second planetary gearset.

In this case, the first and second clutches may be disposed in asequence of the first clutch and the second clutch, in a direction fromthe second planetary gearset to the input shaft.

A one way clutch disposed in parallel with the first brake may befurther included in such an exemplary six-speed powertrain of anautomatic transmission.

The first and second brakes may be realized as wet-type multi-platebrakes or band brakes.

In a wider scope, another exemplary six-speed powertrain of an automatictransmission according to the present invention includes: a firstplanetary gearset having first, second, and third operational elementsthat occupy sequential positions in a lever diagram; a second planetarygearset having fourth, fifth, and sixth operational elements that occupysequential positions in a lever diagram; a third planetary gearsethaving seventh, eighth, and ninth operational elements that occupiessequential positions in a lever diagram; a fourth planetary gearsethaving tenth, eleventh, and twelfth operational elements that occupysequential positions in a lever diagram; an input shaft; an outputshaft; and a transmission case.

The first operational element is fixedly connected to the eighthoperational element and the tenth operational element. The secondoperational element is fixedly connected to the eleventh operationalelement. The fifth operational element is fixedly connected to the ninthoperational element. The fourth operational element is always stationaryby being fixedly connected to the transmission case. The seventhoperational element always acts as an input element by being fixedlyconnected to the input shaft. The eighth operational element always actsas an output element by being fixedly connected to the output gear. Thetwelfth operational element is variably connected to the input shaft viaa first clutch. At least one of the fixedly connected second andeleventh operational elements is variably connected to the input shaftvia a second clutch. The third operational element is variably connectedto the sixth operational element via a third clutch. At least one of thefixedly connected second and eleventh operational elements is variablyconnected to the transmission case via a first brake and is subject to astopping operation of the first brake. The third operational element isvariably connected to the transmission case via a second brake and issubject to a stopping operation of the second brake.

In a further embodiment, the first, second, third, and fourth planetarygearsets are disposed in a sequence of the second planetary gearset, thefirst planetary gearset, the fourth planetary gearset, and the thirdplanetary gearset.

In a still further embodiment, the first operational element of thefirst planetary gearset is integrally formed with the tenth operationalelement of the fourth planetary gearset, and the second operationalelement of the first planetary gearset is integrally formed with theeleventh operational element of the fourth planetary gearset, such thatthe first and fourth planetary gearsets form a compound planetarygearset.

Regarding such an exemplary six-speed powertrain of an automatictransmission, arrangement of the input shaft, the output gear, and thefirst to third clutches may be variously changed.

As a first example, the input shaft is disposed in a same direction ofthe output gear with respect to the third planetary gearset, one of thefirst and second clutches is disposed toward the input shaft withrespect to the third planetary gearset, and another of the first andsecond clutches is disposed opposite of the input shaft with respect tothe second planetary gearset.

In this case, the first clutch may be disposed toward the input shaftwith respect to the third planetary gearset, and the second clutch maybe disposed opposite of the input shaft with respect to the secondplanetary gearset.

As a second example, the input shaft is disposed in a same direction ofthe output gear with respect to the third planetary gearset, and both ofthe first and second clutches are disposed toward the input shaft withrespect to the third planetary gearset.

In this case, the first and second clutches may be disposed in asequence of the first clutch and the second clutch, in a direction fromthe third planetary gearset to the input shaft.

Alternatively in this case, the first and second clutches may bedisposed in a sequence of the second clutch and the first clutch, in adirection from the third planetary gearset to the input shaft.

As a third example, the input shaft is disposed opposite of the outputgear with respect to the second planetary gearset, and both of the firstand second clutches are disposed toward the input shaft with respect tothe second planetary gearset.

In this case, the first and second clutches may be disposed in asequence of the first clutch and the second clutch, in a direction fromthe second planetary gearset to the input shaft.

A one way clutch disposed in parallel with the first brake may befurther included in such an exemplary six-speed powertrain of anautomatic transmission.

The first and second brakes may be realized as wet-type multi-platebrakes or band brakes.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate exemplary embodiments of thepresent invention, and, together with the description, serve to explainthe principles of the present invention, wherein:

FIG. 1 illustrates a six-speed powertrain of an automatic transmissionaccording to a first embodiment of the present invention;

FIG. 2 illustrates a six-speed powertrain of an automatic transmissionaccording to a second embodiment of the present invention;

FIG. 3 illustrates a six-speed powertrain of an automatic transmissionaccording to a third embodiment of the present invention;

FIG. 4 illustrates a six-speed powertrain of an automatic transmissionaccording to a fourth embodiment of the present invention;

FIG. 5 is an operational chart for a six-speed powertrain of anautomatic transmission according to embodiments of the presentinvention;

FIG. 6 is a lever diagram illustrating operational nodes (N1 through N6)of a six-speed powertrain of an automatic transmission according toembodiments of the present invention, in the case that the firstplanetary gearset PG1 and the fourth planetary gearset PG4 have equalring gear/sun gear tooth ratios;

FIG. 7 illustrates a speed diagram for a first forward speed of asix-speed powertrain of an automatic transmission according toembodiments of the present invention;

FIG. 8 illustrates a speed diagram for a second forward speed of asix-speed powertrain of an automatic transmission according toembodiments of the present invention;

FIG. 9 illustrates a speed diagram for a third forward speed of asix-speed powertrain of an automatic transmission according toembodiments of the present invention;

FIG. 10 illustrates a speed diagram for a fourth forward speed of asix-speed powertrain of an automatic transmission according toembodiments of the present invention;

FIG. 11 illustrates a speed diagram for a fifth forward speed of asix-speed powertrain of an automatic transmission according toembodiments of the present invention;

FIG. 12 illustrates a speed diagram for a sixth forward speed of asix-speed powertrain of an automatic transmission according toembodiments of the present invention;

FIG. 13 illustrates a speed diagram for a reverse speed of a six-speedpowertrain of an automatic transmission according to embodiments of thepresent invention;

FIGS. 14A-14F are charts showing operation states obtained when asix-speed powertrain of an automatic transmission according toembodiments of the present invention having specific gear ratios isoperated;

FIG. 15 illustrates an exemplary six-speed powertrain according to theprior art;

FIG. 16 is an operational chart for the powertrain shown in FIG. 15; and

FIGS. 17A-17F are charts showing operation states obtained when thepowertrain shown in FIG. 15 is operated according to the operationalchart in FIG. 16.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An embodiment of the present invention will hereinafter be described indetail with reference to the accompanying drawings.

As shown in FIG. 1 through FIG. 4, a six-speed powertrain of anautomatic transmission according to embodiments of the present inventionincludes four planetary gearsets of first, second, third, and fourthplanetary gearsets PG1, PG2, PG3, and PG3.

The first planetary gearset PG1 is a single pinion planetary gearset,and includes a first sun gear S1, a first carrier PC1, and a first ringgear R1 as operational elements thereof. A first pinion gear P1, beingengaged with both the first ring gear R1 and the first sun gear S1, isconnected to and carried by the first carrier PC1.

The second planetary gearset PG2 is a single pinion planetary gearset,and includes a second sun gear S2, a second carrier PC2, and a secondring gear R2 as operational elements thereof. A second pinion gear P2,being engaged with both the second ring gear R2 and the second sun gearS2, is connected to and carried by the second carrier PC2.

The third planetary gearset PG3 is a single pinion planetary gearset,and includes a third sun gear S3, a third carrier PC3, and a third ringgear R3 as operational elements thereof. A third pinion gear P3, beingengaged with both the third ring gear R3 and the third sun gear S3, isconnected to and carried by the third carrier PC3.

The fourth planetary gearset PG4 is a single pinion planetary gearset,and includes a fourth sun gear S4, a fourth carrier PC4, and a fourthring gear R4 as operational elements thereof. A fourth pinion gear P4,being engaged with both the fourth ring gear R4 and the fourth sun gearS4, is connected to and carried by the fourth carrier PC4.

In addition, as shown in FIG. 1 through FIG. 4, a six-speed powertrainof an automatic transmission according to embodiments of the presentinvention further includes an input shaft 100 for receiving torque froman engine (not shown), an output gear 200 for outputting torque from thepowertrain, and a transmission case 300.

The first ring gear R1 is fixedly connected to the third carrier PC3,and is also fixedly connected to the fourth ring gear R4.

The first carrier PC1 is fixedly connected to the fourth carrier PC4.

The second carrier PC2 is fixedly connected to the third ring gear R3.

The second ring gear R2 is always stationary by being fixedly connectedto the transmission case 300.

The third sun gear S3 always acts as an input element by being fixedlyconnected to the input shaft 100.

The third carrier PC3 always acts as an output element by being fixedlyconnected to the output gear 200.

The fourth sun gear S4 is variably connected to the input shaft 100 viaa first clutch C1.

At least one of the fixedly connected first and fourth carriers PC1 andPC4 is variably connected to the input shaft 100 via a second clutch C2.

The first sun gear S1 is variably connected to the second sun gear S2via a third clutch C3.

At least one of the fixedly connected first and fourth carriers PC1 andPC4 is variably connected to the transmission case 300 via a first brakeB1 and is subject to a stopping operation of the first brake B1.

The first sun gear S1 is variably connected to the transmission case 300via a second brake B2 and is subject to a stopping operation of thesecond brake B2.

As shown in FIG. 1 through FIG. 4, the first, second, third, and fourthplanetary gearsets PG1, PG2, PG3, and PG4 are disposed in a sequence ofthe second planetary gearset PG2, the first planetary gearset PG1, thefourth planetary gearset PG4, and the third planetary gearset PG3.

As shown in FIG. 1 through FIG. 4, regarding the first and fourthplanetary gearsets PG1 and PG4 disposed adjacent to each other betweenthe second and third planetary gearsets PG2 and PG3, the first ring gearR1 of the first planetary gearset PG1 is integrally formed with thefourth ring gear R4 of the fourth planetary gearset PG4. That is, onecommon ring gear CR commonly acts as a ring gear for the first andfourth planetary gearsets PG1 and PG4.

In addition, the first carrier PC1 of the first planetary gearset PG1 isintegrally formed with the fourth carrier PC4 of the fourth planetarygearset PG4. That is, one common pinion carrier CPC commonly acts as acarrier for the first and fourth planetary gearsets PG1 and PG4. Thatis, first pinion gear P1 of the first planetary gearset PG1 and thefourth pinion gear P4 of the fourth planetary gearset PG4 areinterconnected by one common pinion carrier CPC, and they are under thesame operation.

Therefore, the first planetary gearset PG1 and the fourth planetarygearset PG4 form a compound planetary gearset CPG.

Regarding such a compound planetary gearset CPG, in the descriptionhereinafter, the first planetary gearset PG1 and the fourth planetarygearset PG4 are supposed to have the same ring gear/sun gear toothratio.

However, such a supposition is for better description and understandingof the spirit of the present invention, and it should not be understoodthat the scope of the present invention is limited thereto. The firstplanetary gearset PG1 may have a different ring gear/sun gear toothratio from the fourth planetary gearset PG4, and consequences of suchdifference are obvious to a person of ordinary skill in the art from thefollowing description.

As shown in FIG. 1, according to a six-speed powertrain of a firstembodiment of the present invention, the input shaft 100 is disposed ina same direction of the output gear 200 with respect to the thirdplanetary gearset PG3.

In addition, one of the first and second clutches C1 and C2 is disposedtoward the input shaft 100 with respect to the third planetary gearsetPG3. Also, another one of the first and second clutches C1 and C2 isdisposed opposite of the input shaft 100 with respect to the secondplanetary gearset PG2.

In more detail, the first clutch C1 is disposed toward the input shaft100 with respect to the third planetary gearset PG3, and the secondclutch C2 is disposed opposite of the input shaft 100 with respect tothe second planetary gearset PG2.

As shown in FIG. 2 and FIG. 3, according to a six-speed powertrain of asecond or third embodiment of the present invention, the input shaft 100is disposed in a same direction of the output gear 200 with respect tothe third planetary gearset PG3, and both of the first and secondclutches C1 and C2 are disposed toward the input shaft 100 with respectto the third planetary gearset PG3.

As shown, in FIG. 2, according to a six-speed powertrain of a secondembodiment of the present invention, the first and second clutches C1and C2 are disposed in a sequence of the first clutch C1 and the secondclutch C2, in a direction from the third planetary gearset PG3 to theinput shaft 100.

As shown in FIG. 3, according to a six-speed powertrain of a thirdembodiment of the present invention, the first and second clutches C1and C2 are disposed in a sequence of the second clutch C2 and the firstclutch C1, in a direction from the third planetary gearset PG3 to theinput shaft 100.

As shown in FIG. 4, according to a six-speed powertrain of a fourthembodiment of the present invention, the input shaft 100 is disposedopposite of the output gear 200 with respect to the second planetarygearset PG2, and both of the first and second clutches C1 and C2 aredisposed toward the input shaft 100 with respect to the second planetarygearset PG2.

In more detail, according to a six-speed powertrain of a fourthembodiment of the present invention, the first and second clutches C1and C2 are disposed in a sequence of the first clutch C1 and the secondclutch C2, in a direction from the second planetary gearset PG2 to theinput shaft 100.

As shown in FIG. 1 through FIG. 4, a six-speed powertrain of any offirst through fourth embodiment of the present invention furtherincludes a one way clutch OWC disposed in parallel with the first brakeB1.

Due to such a one way clutch OWC, a first forward speed can be realizedby an operation of the third clutch C3 without an operation of the firstbrake B1.

According to a six-speed powertrains of first through fourth embodimentsof the present invention, each of the first and second brakes B1 and B2may by realized by a wet-type multi-plate brake or a band brake.

Hereinafter, an operation of a six-speed powertrain of an automatictransmission according to an embodiment of the present invention isdescribed in detail. The following description may be equally applied tofirst through fourth embodiments of the present invention.

As shown in FIG. 5, a six-speed powertrain of an automatic transmissionaccording to an embodiment of the present invention operates: the thirdclutch C3 and the first brake B1 at a first forward speed D1; the thirdclutch C3 and the second brake B2 at a second forward speed D2; thethird clutch C3 and the first clutch C1 at a third forward speed D3; thethird clutch C3 and the second clutch C2 at a fourth forward speed D4;the first clutch C1 and the second clutch C2 at a fifth forward speedD5; and the second clutch C2 and the second brake B2 at a sixth forwardspeed D6.

The first clutch C1 and the first brake B1 are operated at a reversespeed R.

Specific values of shift ratios shown in FIG. 5 are obtained in the casethat first, second, third, and fourth planetary gearsets PG1, PG2, PG3,and PG4 have ring gear/sun gear tooth ratios as shown in FIG. 14A. Whenthe ring gear/sun gear tooth ratios of the first, second, third, andfourth planetary gearsets PG1, PG2, PG3, and PG4 differ from FIG. 14A,values of shift ratios for the different ring gear/sun gear tooth ratiosmay be obviously calculated by a person of ordinary skill in the artfrom the detailed description of the present invention.

FIG. 6 is a lever diagram illustrating operational nodes (N1 through N6)of a six-speed powertrain of an automatic transmission according toembodiments of the present invention, in the case that the firstplanetary gearset PG1 and the fourth planetary gearset PG4 have equalring gear/sun gear tooth ratios.

Therefore, operational elements of the fourth planetary gearset PG4 showrotational characteristics equal to operational elements of the firstplanetary gearset PG1. Therefore, they may be represented by operationalelements of the first planetary gearset PG1 and be disregardedhereinafter.

As shown in FIG. 6, the first ring gear R1, the first carrier PC1, andthe first sun gear S1 of the first planetary gearset PG1 aresequentially located at operational nodes N2, N4, and N6 in the leverdiagram.

The second ring gear R2, the second carrier PC2, and the second sun gearS2 of the second planetary gearset PG2 are sequentially located atoperational nodes N3, N5, and N6 in the lever diagram.

The third sun gear S3, the third carrier PC3, and the third ring gear R3of the third planetary gearset PG3 are sequentially located atoperational nodes N1, N2, and N5 in the lever diagram.

The fourth ring gear R4, the fourth carrier PC4, and the fourth sun gearS4 of the fourth planetary gearset PG4 are sequentially located atoperational nodes N2, N4, and N6 in the lever diagram.

As described above, the input shaft 100 is variably connected to thefourth sun gear S4 and the first carrier PC1 (or equivalently, thefourth carrier PC4) via the first and second clutches C1 and C2,respectively. Therefore, engine rotation input through the input shaft100 is delivered to the sixth node N6 or the fourth node N4 according toan operation of the first and second clutches C1 and C2, respectively.

The first carrier PC1 (or equivalently, the fourth carrier PC4) isvariably connected to the transmission case 300 via the first brake B1and the one way clutch OWC disposed in parallel. Therefore, the fourthnode N4 of the first carrier PC1 and the fourth carrier PC4 may bestopped by an operation of the first brake B1 and/or the one way clutchOWC.

In addition, the first sun gear S1 is variably connected to thetransmission case 300 via the second brake B2. Therefore, the sixth nodeN6 may be stopped by an operation of the second brake B2.

Hereinafter, formation of each speed by a six-speed powertrain of anautomatic transmission according to an embodiment of the presentinvention is described in detail with reference to FIGS. 7-13.

In FIG. 7 through FIG. 13, L1 denotes a speed line for the firstplanetary gearset PG1, L2 denotes a speed line for the second planetarygearset PG2, and L3 denotes a speed line for the third planetary gearsetPG3.

The speed line L1 of the first planetary gearset PG1 and the speed lineL3 of the third planetary gearset PG3 meet at the second node N2 sincethe first ring gear R1 and the third carrier PC3 are fixedlyinterconnected.

The speed line L2 of the second planetary gearset PG2 and the speed lineL3 of the third planetary gearset PG3 meet at the fifth node N5, sincethe second carrier PC2 and the third ring gear R3 are fixedlyinterconnected.

The third node N3 is always stationary since the second ring gear R2 isfixedly connected to the transmission case 300.

The third sun gear S3 always rotates at an input speed since it isfixedly connected to the input shaft.

Arrangement of the speed lines L1, L2, and L3 of the first, second, andthird planetary gearsets PG1, PG2, and PG3 are determined by selectiveoperation of the first, second, and third clutches C1, C2, and C3 andthe first and second brakes B1 and B2 under such a condition.

At the first forward speed D1, as shown in FIG. 7, the first sun gear S1and the first sun gear S1 on the sixth node N6 rotate at a synchronizedspeed since the third clutch C3 operates. In addition, the fourth nodeN4 is stationary since the first brake B1 operates.

Therefore in this case, the speed lines L1, L2, and L3 are formed asshown in FIG. 7.

That is, regarding the third, fifth, and sixth nodes N3, N5, and N6 ofthe second planetary gearset PG2, the third node N3 is stationary, andthe fifth and sixth nodes N5 and N6 rotate at a negative speed, i.e., inreverse.

Regarding the second, fourth, and sixth nodes N2, N4, and N6 of thefirst planetary gearset PG1, the speed line L1 is a line connecting thesixth node N6 that is rotating in reverse and the fourth node N4 that isstationary.

Therefore, the speed line L3 of the third planetary gearset PG3 isformed to be declining rightward as shown in FIG. 7. In this case, anoutput element of the third carrier PC3 rotates at a very low speedrelative to a rotation of the input shaft 100.

At such a first forward speed, all the first, second, and thirdplanetary gearsets PG1, PG2, and PG3 take part in the powertransmission.

At the second forward speed D2, as shown in FIG. 8, the first sun gearS1 and the first sun gear S1 on the sixth node N6 remain rotating at asynchronized speed since the third clutch C3 also operates in the secondforward speed. In addition, the sixth node N6 is stationary since thesecond brake B2 operates.

Therefore in this case, the second carrier PC2, i.e., the fifth node N5,of the second planetary gearset PG2 becomes stationary since both thethird and sixth nodes N3 and N6 are stationary. This implies that thefifth node N5 is also stationary.

Therefore, the speed line L3 of the third planetary gearset PG3 isformed by the fifth node N5 that is stationary and the first node N1rotating at the input speed. Such a speed line L3 of the third planetarygearset PG3 becomes slightly rotated counterclockwise, in comparisonwith the first forward speed. Therefore, the third carrier PC3 that isan output element rotates at an increased speed in comparison with thefirst forward speed.

At such a second forward speed, only the third planetary gearset PG3takes part in the power transmission since the second planetary gearsetPG2 is stationary.

At the third forward speed D3, as shown in FIG. 9, the first sun gear S1and the first sun gear S1 on the sixth node N6 remain rotating at asynchronized speed since the third clutch C3 also operates in the thirdforward speed. In addition, the sixth node N6 also rotates at the samespeed as the input shaft 100 since the first clutch C1 operates.

Therefore in this case, the speed line L2 of the second planetarygearset PG2 is formed by the third node N3 that is stationary and thesixth node N6 rotating at the input speed. The drive line L3 of thethird planetary gearset PG3 is determined by the fifth node N5 on thespeed line L2 of the second planetary gearset PG2.

Therefore, the speed line L3 of the third planetary gearset PG3 becomesslightly rotated counterclockwise, in comparison with the second forwardspeed. Therefore, the third carrier PC3 that is an output elementrotates at an increased speed in comparison with the second forwardspeed.

At such a third forward speed, the second and third planetary gearsetsPG2 and PG3 take part in the power transmission.

At the fourth forward speed D4, as shown in FIG. 10, the first sun gearS1 and the first sun gear S1 on the sixth node N6 remain rotating at asynchronized speed since the third clutch C3 also operates in the fourthforward speed. In addition, the fourth node N4 also rotates at the samespeed as the input shaft 100 since the second clutch C2 operates.

Therefore in this case, the speed lines L1, L2, and L3 are formed asshown in FIG. 10.

That is, the speed line L2 of the second planetary gearset PG2 becomesslightly rotated counterclockwise, in comparison with the third forwardspeed.

In the same way, the speed line L3 of the third planetary gearset PG3becomes slightly rotated counterclockwise, in comparison with the thirdforward speed. Therefore, the third carrier PC3 that is an outputelement rotates at an increased speed in comparison with the thirdforward speed.

At such a fourth forward speed, all the first, second, and thirdplanetary gearsets PG1, PG2, and PG3 take part in the powertransmission.

At the fifth forward speed D5, the first and second clutches C1 and C2operate. Therefore, as shown in FIG. 11, the fourth and sixth nodes N4and N6 rotate at the same speed as the input shaft 100.

That is, the first carrier PC1 and the first sun gear S1 of the firstplanetary gearset PG1 rotate at an input speed.

Therefore, the speed line L1 of the first planetary gearset PG1 becomeshorizontal at a height of rotation speed of the input shaft 100. Thisimplies that the first planetary gearset rotates as a whole.

Therefore, the second node N2 also rotates at the input speed, andaccordingly, the input speed is directly output without changing.

At such a fifth forward speed, none of the first, second, and thirdplanetary gearsets PG1, PG2, and PG3 takes part in the powertransmission.

At the sixth forward speed D6, as shown in FIG. 12, the fourth node N4rotates at the same speed as the input shaft 100 since the second clutchC2 operates. In addition, the first sun gear S1 of the sixth node N6becomes stationary since the second brake B2 operates.

The speed line L1 of the first planetary gearset PG1 is formed by thesixth node N6 that is stationary and the fourth node N4 rotating at theinput speed.

Therefore, the second node N2 on the speed line L1 of the firstplanetary gearset PG1 rotates at a speed higher than the input speed.This implies that rotation speed output from the third carrier PC3 ishigher than the input speed.

At such a sixth forward speed, only the first planetary gearset PG1takes part in the power transmission.

At the reverse speed R, the first clutch C1 and the first brake B1operate. Therefore, as shown in FIG. 13, the speed line L1 of the firstplanetary gearset PG1 is formed by the fourth node N4 that is stationaryand the sixth node N6 rotating at the input speed.

Therefore, the second node N2 on the speed line L1 of the firstplanetary gearset PG1 rotates at a negative speed, i.e., rotatesreversely, as shown in FIG. 13.

At such a sixth forward speed, only the first planetary gearset PG1takes part in the power transmission.

FIGS. 14A-14F are charts showing operation states of a power train of anautomatic transmission according to a preferred embodiment of thepresent invention.

In particular, FIG. 14A shows detailed specifications of the powertrainaccording to one embodiment, i.e., gear ratios of each planetarygearset. FIG. 14B shows speed ratios in each shift-speed of thepowertrain of such an embodiment obtained by the detailed specificationof FIG. 14A. FIG. 14C shows rotation speeds of each operational elementrelative to that of the input element, for each shift-speed. FIG. 14Dshows slip speeds of friction elements at each shift-speed. FIG. 14Eshows torque loads that each operational element or each frictionelement undertakes. FIG. 14F shows planetary gearsets that take part inpower transmission in each shift-speed.

Details shown in FIG. 14F are apparent from the above description ofshifting operation of the powertrain of the present invention, and thenumbers shown in FIGS. 14C-14E may be calculated by a person skilled inthe art based on the structural features and operational chart of thepowertrain of the present embodiment.

As is well known in the art, under hard acceleration, a high load isinput to an automatic transmission. According to powertrains ofpreferred embodiments, no operational element rotates faster than theinput speed at the second and third speeds that are frequently engagedfor acceleration (refer to FIG. 14C), and therefore, slip speeds offriction elements not operated at the third speed are less than therotation speed of the input shaft (refer to FIG. 14D).

When the performance shown in FIG. 14D is compared with performance of aprior art powertrain shown in FIG. 17D, it is apparent that thepowertrains of the present embodiments show less slip speeds of frictionelements overall at the second to sixth speeds (especially at sixthforward speed) than the powertrain of, for example, U.S. Pat. No.6,071,208.

Also, it is well known that more planetary gearsets implies more loss ofpower during power transmission. When the performance shown in FIG. 14Fis compared with performance of the prior art powertrain shown in FIG.17F, it is apparent that the powertrains of the preferred embodimentshave less planetary gearsets involved in the power transmission at manyof the shift-speeds, and accordingly they show better power efficiency.

According to a preferred embodiment of the present invention, sixforward speeds and one reverse speed are achieved with a minimizednumber of friction elements such that an automatic transmission becomeslighter and more compact.

Durability is increased due to reduction of rotation speeds ofoperational elements at a shift-speed frequently engaged foracceleration. A further increase of durability and reduction of powerloss is also achieved by reduction of slip speeds of friction elements.

A shortened route of power transmission also contributes to an increaseof durability and reduction of power loss.

A shortened route of power transmission also contributes to an increaseof durability and reduction of power loss.

In addition, torque load is dispersed to all operating elements of aplanetary gearset, and accordingly the powertrain may endure higherload.

While this invention has been described in connection with what ispresently considered to be the most practical exemplary embodiments, itis to be understood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A six-speed powertrain of an automatic transmission, comprising: afirst planetary gearset having operational elements of a first sun gear,a first ring gear, and a first carrier; a second planetary gearsethaving operational elements of a second sun gear, a second ring gear,and a second carrier; a third planetary gearset having operationalelements of a third sun gear, a third ring gear, and a third carrier; afourth planetary gearset having operational elements of a fourth sungear, a fourth ring gear, and a fourth carrier; an input shaft; anoutput gear; and a transmission case, wherein: the first ring gear isfixedly connected to the third carrier and the fourth ring gear; thefirst carrier is fixedly connected to the fourth carrier; the secondcarrier is fixedly connected to the third ring gear; the second ringgear is always stationary by being fixedly connected to the transmissioncase; the third sun gear always acts as an input element by beingfixedly connected to the input shaft; the third carrier always acts asan output element by being fixedly connected to the output gear; thefourth sun gear is variably connected to the input shaft via a firstclutch; at least one of the fixedly connected first and fourth carriersis variably connected to the input shaft via a second clutch; the firstsun gear is variably connected to the second sun gear via a thirdclutch; at least one of the fixedly connected first and fourth carriersis variably connected to the transmission case via a first brake and issubject to a stopping operation of the first brake; and the first sungear is variably connected to the transmission case via a second brakeand is subject to a stopping operation of the second brake.
 2. Thepowertrain of claim 1, wherein the first, second, third, and fourthplanetary gearsets are disposed in a sequence of the second planetarygearset, the first planetary gearset, the fourth planetary gearset, andthe third planetary gearset.
 3. The powertrain of claim 2, wherein: thefirst ring gear of the first planetary gearset is integrally formed withthe fourth ring gear of the fourth planetary gearset; and the firstcarrier of the first planetary gearset is integrally formed with thefourth carrier of the fourth planetary gearset, such that the first andfourth planetary gearsets form a compound planetary gearset.
 4. Thepowertrain of claim 3, wherein the input shaft is disposed in a samedirection of the output gear with respect to the third planetarygearset; one of the first and second clutches is disposed toward theinput shaft with respect to the third planetary gearset; and another oneof the first and second clutches is disposed opposite of the input shaftwith respect to the second planetary gearset.
 5. The powertrain of claim4, wherein: the first clutch is disposed toward the input shaft withrespect to the third planetary gearset; and the second clutch isdisposed opposite of the input shaft with respect to the secondplanetary gearset.
 6. The powertrain of claim 3, wherein: the inputshaft is disposed in a same direction of the output gear with respect tothe third planetary gearset; and both of the first and second clutchesare disposed toward the input shaft with respect to the third planetarygearset.
 7. The powertrain of claim 6, wherein the first and secondclutches are disposed in a sequence of the first clutch and the secondclutch, in a direction from the third planetary gearset to the inputshaft.
 8. The powertrain of claim 6, wherein the first and secondclutches are disposed in a sequence of the second clutch and the firstclutch, in a direction from the third planetary gearset to the inputshaft.
 9. The powertrain of claim 3, wherein: the input shaft isdisposed opposite of the output gear with respect to the secondplanetary gearset; and both of the first and second clutches aredisposed toward the input shaft with respect to the second planetarygearset.
 10. The powertrain of claim 9, wherein the first and secondclutches are disposed in a sequence of the first clutch and the secondclutch, in a direction from the second planetary gearset to the inputshaft.
 11. The powertrain of claim 1, further comprising a one wayclutch disposed in parallel with the first brake.
 12. The powertrain ofclaim 1, wherein the first and second brakes are wet-type multi-platebrakes or band brakes.